Apple has started seeding OS X Mountain Lion 10.8.5 beta 12F17 (third beta build) today to developers. The changelog does not list any known issues.

These betas are being released for an upcoming update of OS X Mountain Lion, which will bring the version number up to 10.8.5. Despite having already announced OS X Mavericks, the particular Mac version is the one that’s publicly available right now. Mavericks is expected to be released this fall. Mountain Lion continues to be supported and the imminent update is going to bring a host of bug fixes as well as performance improvements.

When Apple seeded the first beta of OS X 10.8.5 Mountain Lion to developers, it advised them to focus their work on Mobile Device Management, PDF viewing and Accessibility, Wi-Fi, Graphics and Wake from Sleep. In this particular build as well, 12F17 to be precise, the same instructions have been handed down to developers. If they find any bugs related to these features or the whole OS in general, they can report them to Apple.

This build is only available for developers right now, since OS X 10.8.5 is actually an incremental update for Mountain Lion, it shouldn’t take more than a couple of weeks for this update to exit beta stage and enter public roll out. We’ll let you know when that happens.